1. Field of the Invention
The present invention relates to a time-division multiplex communication system comprising a transmitting device which regularly inserts an n-bit word coded in a linear block code into the bit sequence to be transmitted, and a checking device at the receiving end which looks for the n-bit word in the received bit sequence by checking groups of n successive bits as to whether they are coded in the block code.
2. Description of the Prior Art
Such a system is disclosed in DE-A1-37 35 377, wherein a so-called code word is derived from information referred to there as "header", which contains a logic channel number, and transmitted subsequent to the information. In common technical terms, the information (K) is coded in a linear block code to form a code word whose number of bits is equal to the number of bits of the information (K) augmented by the number of added bits (called "code word CW" there) . The number of bits in the code word consisting of the k-bit information (K) and the added bits will hereinafter be denoted by n. In the prior art system, such code words are inserted at the transmitting end into the bit sequence at regular time intervals, namely at the beginning of each so-called packet. At the receiving end, the prior art system includes a checking device which looks for the n-bit code words in the received bit sequence. It does so by selecting a sequence of k-bits from the received bit sequence and checking whether this k-bit sequence and the subsequently received n-k bits (n-k is the number of bits added to the information K at the transmitting end) together represent a code word which is coded in the block code. If the checking device determines that the checked bit sequence is not coded in the block code, it will stop the search for the code word in the current packet and resume it in the next packet, in which it then selects a bit sequence which, referred to the beginning of the packet, begins one bit later than the bit sequence selected in the previously checked packet.
This means that considerable time may elapse until the n-bit word looked for is found in any packet. This, in turn, has the disadvantage that the synchronization of the receiver with the transmitter takes a long time, thus causing considerable information losses.